No abstract

Poly(dimethylsiloxane) (PDMS) appeared recently as a material of choice for rapid and accurate replication of polymer-based microfluidic networks. However, due to its hydrophobicity, the surface strongly interacts with apolar analytes or species containing apolar domains, resulting in significant uncontrolled adsorption on channel walls. This contribution describes the application and characterization of a PDMS surface treatment that considerably decreases adsorption of low and high molecular mass substances to channel walls while maintaining a modest cathodic electroosmotic flow. Channels are modified with a three-layer biotin-neutravidin sandwich coating, made of biotinylated IgG, neutravidin, and biotinylated dextran. By replacing biotinylated dextran with any biotinylated reagent, the modified surface can be readily patterned with biochemical probes, such as antibodies. Combination of probe immobilization chemistry with low nonspecific binding enables affinity binding assays within channel networks. The example of an electrokinetic driven, heterogeneous immunoreaction for human IgG is described.

A theoretical description of the steady-state potential response of ionophore-based ion-selective electrodes is presented that, so far, is the most general formalism available. The treatment considers membrane systems with any number of ionophores, differently charged cations, anions, and fixed or stationary ionic sites. The theory accounts for thermodynamically controlled selectivity characteristics, as well as for various diffusion-induced effects resulting from transmembrane ion fluxes at zero current. The phenomena discussed in detail include apparent super- and sub-Nernstian responses and detection limits. An extension of the treatment for time-dependent phenomena is also given. The present approach can be applied for optimizing the selectivity coefficients and improving the detection limits of ionophore-based ion-selective electrodes.